Download A Model of Three Faults

A Model of Three Faults
Adapted from the USGS Learning Web Lesson Plans
Background: One of the most frightening and destructive phenomena of nature is a severe
earthquake and its terrible after-effects. An earthquake is a sudden movement of the Earth,
caused by the abrupt release of strain that has accumulated over a long time. For hundreds of
millions of years, the forces of plate tectonics have shaped the Earth as the huge plates that
form the Earth's surface slowly move over, under and past each other. Sometimes the
movement is gradual. At other times, the plates are locked together, unable to release the
accumulating energy. When the accumulated energy grows strong enough, the plates break
free. If the earthquake occurs in a populated area, it may cause many deaths and injuries and
extensive property damage.
Today we are challenging the assumption that earthquakes must present an uncontrollable and
unforecastable hazard to life and property. Scientists have begun to estimate the locations and
likelihoods of future damaging earthquakes. Sites of greatest hazard are being identified, and
designing structures that will withstand the effects of earthquakes.
Objective: Students will observe fault movements on a model of the earth's surface.
Materials Needed (per group)
 Crayons or colored pencils
 Scissors
 Tape or glue
 Metric ruler
 Fault Model Sheet (included)
Instructions
1. Students can work in pairs or small groups.
2. Display the fault models in the classroom after the activity.
3. An excellent world physiographic map, showing the ocean floor, can be obtained from
the National Geographic Society.
Faults are often (but not always) found near plate boundaries and that each type of fault is
frequently associated with specific types of plate movements. However, you can probably find
all types of fault movement associated with each type of plate boundary.
 Normal faults are often associated with divergent (tensional) boundaries.
 Thrust faults are often associated with convergent (compressional) boundaries.
 Strike-slip faults are often associated with transform (sliding) boundaries.
Answer the following questions:
1. What kind of faults would you expect to find in the Himalaya Mountains? Why?
2. What kind of faults would you expect to find along the Mid-Atlantic Ridge? Why?
3. What kind of fault is the San Andreas Fault? Is California likely to "fall off into the Pacific
Ocean"? Why?
Not all faults are associated with plate boundaries. There is a broad range of faults based on
type, linear extension, displacement, age, current or historical activity and location on
continental or oceanic crust. The stresses and strains in the earth's upper layers are induced by
many causes: thermal expansion and contraction, gravitational forces, solid-earth tidal forces,
specific volume changes because of mineral phase transitions, etc. Faulting is one of the
various manners of mechanical adjustment or release of such stress and strain. Fault
movement is classified as normal, reverse, or strike-slip.
Answer the following question:
4. Use your book and other resources to identify the fault movements in the following
earthquakes that occurred far from any plate boundary:
a. Fort Collins, Colorado, November 1882
b. New Madrid, Missouri, December 1811
c. West Yellowstone, Montana, August 1959
d. Virginia, August 23, 2011
Constructing a fault model using the Fault Model Sheet
Color the fault model that is included according to the color key provided.
o Cut out the fault model and fold each side down to form a box with the drawn features on
top.
o Tape or glue the corners together. This box is a three dimensional model of the top
layers of the Earth's crust.
o The dashed lines on your model represent a fault. Carefully cut along the dashed lines.
You will end up with two pieces.
Modeling a normal fault.
o Locate points A and B on your model. Move point B so that it is next to Point A.
o Observe your model from the side (its cross-section).
o Draw the fault as represented by the model you have just constructed and label the type
of fault.
Answer the following questions:
5. Which way did point B move relative to point A?
6. What happened to rock layers X, Y and Z?
7. Are the rock layers still continuous?
8. What likely happened to the river? the road? the railroad tracks?
9. Is this type of fault caused by tension, compression or shearing?
10. Nevada has hundreds of faults of this type. What would cause this?
Modeling a thrust fault.
 Locate points C and D on your model.
 Move Point C next to point D.
 Observe the cross-section of your model.
 Draw the fault as represented by the model you have just constructed and label the type
of fault.
Answer the following questions:
11. Which way did point D move relative to point C?
12. What happened to rock layers X, Y and Z?
13. Are the rock layers still continuous?
14. What likely happened to the river? the road? the railroad tracks?
15. Is this type of fault caused by tension, compression or shearing?
16. During the Northridge, California earthquake, the mountains were raised by as much as
70 cm and moved up to 10 cm closer to the city. Explain how this movement is similar to
the model you just created.
Modeling a strike-slip fault.
 Locate points F and G on your model.
 Move the pieces of the model so that point F is next to point G.
 Draw an overhead view of the surface as it looks after movement along the fault.
 Label the fault type.
Answer the following questions
17. If you were standing at point F and looking across the fault, which way did the block on
the opposite side move?
18. What happened to rock layers X, Y, and Z?
19. Are the rock layers still continuous?
20. What likely happened to the river? the road? the railroad tracks?
21. If the scale used in this model is 1 mm = 2 m, how many meters did the earth move
when the strike-slip fault caused point F to move alongside point G? (Note that this scale
would make an unlikely size for the railroad track! If there were a sudden horizontal shift
of this magnitude it would be about five times the shift that occurred in the 1906 San
Andreas fault as a result of the San Francisco earthquake.)
22. Is this type of fault caused by tension, compression or shearing?
23. This type of fault can be described as having right or left-lateral movement. If you look
directly across the fault, the direction that the opposite side moved defines whether the
movement is left-lateral or right-lateral. Is the San Andreas fault in California right-lateral
or left-lateral?.